Mesenchymal stem cells (MSCs) based bone tissue engineering has become a potential alternative approach for craniofacial skeletal defect repair. Bone regeneration and integration are influenced both by properties of tissue-engineered constructs and pathophysiological environments of implantation sites. For practical clinical application, a stimulus to improve effectively the differentiation potentials of MSCs is demanded. Current positive outcomes of bone tissue engineering have been established utilizing young and healthy hosts. The influence of pathophysiological conditions such as osteoporosis on bone formation and integration of engineered bone is still elusive. Estrogen has been known to inhibite bone resorption and increase bone formation. It was found recently that estrogen can improve osteogenic differentiation of bone marrow MSCs. We hypothesize that estrogen can be employed to up-regulate osteogenic potential of MSCs for optimizing tissue-engineered constructs in vitro and to improve bone formation and osteo-integration in vivo. The overall objective of this project is to optimize estrogen modulation of tissue-engineered constructs and investigate bone formation of optimized constructs at different host environments. Effects of estrogen of various concentrations will be assessed for differentiation of MSCs-based constructs in vitro (Aim 1) and bone formation in vivo (Aim 2). Bone regeneration and integration of optimized constructs will be evaluated in femur bone defects in hosts with different estrogen levels (Aim 3). This project will provide important information for clinical applications of bone tissue engineering. The obtained data during this R03 grant will be included in to an R01 application striving to optimize the properties of MSCs-based constructs and pathophysiological environments for skeletal tissue engineering. PHS 398/2590 (Rev. 09/04, Reissued 4/2006) Page Continuation Format Page This project will provide crucial information of estrogen on bone tissue engineering for clinical application. The current project is to explore estrogen as a modulator to improve mesenchymal stem cell (MSC)-based bone formation. We will investigate estradiol to modulate MSCs-based tissue engineered constructs in vitro and to improve the bone formation and osteo-integration in osteoporotic environments. [unreadable] [unreadable] [unreadable]